1. Field of the Invention
The present disclosure relates generally to a fluid pressure control apparatus and, more particularly, to an automatic tire inflation device that is mounted on a dual wheel unit of a vehicle for maintaining a desired inflation pressure within a pair of tires mounted on the dual wheel unit.
2. Related Art
This section provides background information related to the present disclosure which is not necessarily prior art.
Maintaining correct inflation pressure in vehicle tires is known to be an effective way to increase fuel economy, decrease tire wear and increase safety. Optimum fuel economy results when vehicle tires are inflated to the proper pressure where the rolling resistance of the tire is minimized. Tire over-inflation causes excessive wear near the middle of the tire's tread due to the tire bulging outward. On the other hand, under-inflation results in excessive wear at the edges of the tire's tread as the tire flattens. It is estimated that improper tire inflation results in billions of dollars of unnecessary tire wear each year in the United States, as well as increasing fuel consumption by about 3% and producing an additional 1400 kilograms of CO2 emissions per vehicle.
An automobile tire may lose one to two psi of pressure per month in cool weather and more in warmer weather. Additionally, tire pressure varies with the temperature of air in the tire and is consequently affected by vehicle speed, road surface, ambient temperature, etc. Although proper tire inflation may be maintained by regularly checking tire pressure and adjusting accordingly, such maintenance tends to be largely ignored because of the inconvenience that is involved.
A number of systems are known for automatically maintaining tire inflation pressure during the operation of a motorized vehicle. These known systems may be grouped into two broad categories: centralized systems and on-wheel systems. Centralized systems are installed typically on commercial vehicles, such as for instance tractor trailers, and they feed air from a central air tank or compressor to each of the vehicles rotating tires via rotary pneumatic joints and seals. Of course, the use of such rotary seals involves several inherent disadvantages. For instance, installation and maintenance are complex and costly. Further, such rotary joints and seals are necessarily operated in an environment that is inherently hostile to their performance. As such, centralized systems for automatically maintaining tire inflation are not generally considered to be a practical solution for use in automobiles, with the exception of a few high-end luxury brands.
Various on-wheel (or in-wheel) systems are also known. In these systems, a separate inflation mechanism is carried on each wheel of the vehicle such that the pressure of each tire is adjusted using a mechanism that is mounted to the same wheel to which the tire is mounted. Tire deformation-based systems, such as the one disclosed in U.S. Pat. No. 5,975,174, may include a compressor disposed inside the tire and a plunger for converting deformation of the rotating tire into a linear force for driving a piston of the compressor. Of course, the mechanism is not user-serviceable and is generally inaccessible, requiring the tire to be removed each time maintenance is performed. Alternatively, a wheel-mounted, centrifugally activated air compressor for adjusting tire pressure is disclosed in U.S. Patent Application Publication No. 2011/0129360. The system disclosed uses a plurality of pistons and spring-biased centrifugal arms to adjust the pressure of each tire. Not only is the system overly complicated, it is also susceptible to mechanical failure under the harsh operating conditions typically found in the vicinity of vehicle wheels.
Accordingly, it would be advantageous to provide a tire inflation apparatus that overcomes at least some of the above-mentioned limitations of the prior art. Further, it would be advantageous to provide a tire inflation apparatus that can be used on dual wheel units of vehicles.